Ports Configuration
The 16 I/O ports P0 through P15 can be configured to
any combination of inputs and outputs using the ports
configuration registers (Table 5). The INT/O16 output
can also be configured as an extra general-purpose
output using the configuration register (Table 4).
Input Ports
The input ports registers are read only (Table 6). They
reflect the incoming logic levels of the ports, regardless
of whether the port is defined as an input or an output
by the ports configuration registers. Reading an input
ports register latches the current-input logic level of the
affected eight ports. A write to an input ports register is
ignored.
Transition Detection
All ports configured as inputs are always monitored for
changes in their logic status. The action of reading an
input ports register or writing to the configuration regis-
ter samples the corresponding 8 port bits’ input condi-
tion (Tables 4, 6). This sample is continuously
compared with the actual input conditions. A detected
change in input condition causes an interrupt condition.
The interrupt is cleared either automatically if the
changed input returns to its original state, or when the
appropriate input ports register is read, updating the
compared data (Figure 10). Randomly changing a port
from an output to an input may cause a false interrupt
to occur if the state of the input does not match the
content of the appropriate input ports register. The
interrupt status is available as the interrupt flag INT in
the configuration register (Table 4).
The input status of all ports are sampled immediately
after power-up as part of the MAX7313’s internal initial-
ization, so if all the ports are pulled to valid logic levels
at that time an interrupt does not occur at power-up.
INT/O16 Output
The INT/O16 output pin can be configured as either the
INT output that reflects the interrupt flag logic state or
as a general-purpose output O16. When used as a
general-purpose output, the INT/O16 pin has the same
blink and PWM intensity control capabilities as the
other ports.
Set the interrupt enable I bit in the configuration register
to configure INT/O16 as the INT output (Table 4). Clear
interrupt enable to configure INT/O16 as the O16. O16
logic state is set by the 2 bits O1 and O0 in the configu-
ration register. O16 follows the rules for blinking select-
ed by the blink enable flag E in the configuration
register. If blinking is disabled, then interrupt output
control O0 alone sets the logic state of the INT/O16 pin.
MAX7313
16-Port I/O Expander with LED Intensity
Control, Interrupt, and Hot-Insertion Protection
______________________________________________________________________________________ 13
Table 2. Register Address Map
